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| Chubut Group | |
|---|---|
| Name | Chubut Group |
| Type | Stratigraphic group |
| Period | Cretaceous–Paleogene |
| Prange | Late Cretaceous–Paleogene |
| Region | Patagonia, Argentina |
| Country | Argentina |
Chubut Group is a Mesozoic–Paleogene stratigraphic succession in central and northern Chubut Province, Santa Cruz Province, and Río Negro Province of Argentina within Patagonia. It comprises continental and marginal marine units that have been studied in relation to regional tectonics involving the Andes Mountains, basin evolution of the Golfo San Jorge Basin, and biotic turnovers linked to the Cretaceous–Paleogene extinction event and South American paleobiogeography.
The succession sits within the sedimentary architecture of the Golfo San Jorge Basin, overlying older Paleozoic basement related to the Famatinian Orogeny and underlying Tertiary cover sequences tied to Andean orogeny phases. Stratigraphic subdivision traditionally separates multiple formations and members distributed across outcrops near the Chubut River, Paso del Sapo, and coastal cliffs at Puerto Madryn and Bahía Blanca, and correlates with units mapped in the Neuquén Basin and Magallanes Basin. Regional mapping by Argentine geological surveys and researchers from institutions such as the Consejo Nacional de Investigaciones Científicas y Técnicas and the Universidad Nacional de la Patagonia San Juan Bosco has refined lithostratigraphic contacts and unconformities associated with the Campanian, Maastrichtian, and early Paleogene stages.
Lithofacies include fluvial sandstones, overbank mudstones, conglomerates, paleosols, and localized tuffaceous horizons tied to volcanic activity from the Patagonian Volcanic Province and intrusive episodes related to the Andean magmatic arc. Grain-supported conglomerates with clasts sourced from Precordillera terrains alternate with trough-cross-bedded sandstones indicating channelized flow linked to the South American Plate interior drainage evolution. Siliciclastic strata show pedogenic carbonate nodules, root traces, and calcrete horizons comparable to continental successions in the Eocene of Patagonia and volcaniclastics bearing phenocrysts similar to those in the Choiyoi Group.
Fossil assemblages include diverse vertebrates such as non-avian dinosaurs (including titanosaurian sauropods and megaraptorids), early birds, crocodyliforms, turtles, and mammals tied to Gondwanan faunal provinces including taxa comparable to finds from the Allen Formation, Maastrichtian units of Uruguay, and the Los Alamitos Formation. Ichnofossils include dinosaur tracks and invertebrate trace makers comparable to ichnotaxa described from the Bajo de la Carpa Formation and Candeleros Formation. Plant macrofossils and palynological records document angiosperm, fern, and gymnosperm elements that inform correlations with palynofloras from New Zealand and Antarctica during the Late Cretaceous and early Paleocene.
Biostratigraphic indicators, palynology, magnetostratigraphy, and radiometric dates from interbedded volcanic ashes provide age constraints spanning the Campanian through the Danian and into the Paleocene across different localities, allowing correlation with coeval South American units such as the Los Alamitos Formation, the Allen Formation, and the Loncoche Formation. Correlations extend to southern high-latitude successions in Antarctic Peninsula and to Gondwanan sequences in Australia via shared palynological and vertebrate taxa; these correlations have implications for reconstructions of South Atlantic opening and regional faunal dispersal.
Facies analysis indicates deposition in fluvial braid-plain, meandering floodplain, lacustrine, and marginal coastal settings influenced by eustatic variations of the South Atlantic Ocean and regional tectonic subsidence. Paleogeographic reconstructions place the succession within subtropical to temperate paleolatitudes of southern Gondwana during the Late Cretaceous–Paleogene transition, with climate signals comparable to contemporaneous records from Patagonia, Antarctic Peninsula, and New Zealand. Syn-depositional volcanism and ash-fall events tied to the Patagonian Magmatic Province created tephra layers used for chronostratigraphy and affected local ecosystems similarly to volcanic perturbations documented in the Deccan Traps–adjacent records.
Sedimentary reservoirs in the wider Golfo San Jorge Basin host hydrocarbons exploited by companies such as YPF and international partners, and the group’s sandstones and conglomerates have been evaluated for reservoir potential and aquifer properties in basin modeling by petroleum geologists. Secondary resources include construction-grade aggregates and paleosol-hosted calcretes used regionally, while fossil localities contribute to geotourism and paleontological tourism promoted by provincial cultural agencies and museums such as the Museo Paleontológico Egidio Feruglio and the Museo Provincial de Ciencias Naturales e Historia de San Fernando del Valle de Catamarca.
Early geological descriptions in the late 19th and early 20th centuries by explorers and geologists working in Patagonia, including surveys by the Servicio Geológico Minero Argentino and academic teams from the Universidad de Buenos Aires, led to initial mapping and nomenclature. Subsequent systematic work by paleontologists and stratigraphers affiliated with institutions like the American Museum of Natural History, Natural History Museum, London, and regional universities refined the group’s subdivisions, while modern multidisciplinary studies continue through collaborations involving the Smithsonian Institution, CONICET, and international research programs focused on Gondwanan paleobiology and basin analysis.
Category:Geologic formations of Argentina Category:Patagonia